Heat a large pot over medium and add oil.
Add onions with a sprinkle of salt, cooking until onions are translucent. About 5 minutes.
Add celery and carrots, cook 2-3 minutes, or until softened.
Add garlic, cooking 1-2 minutes.
Sprinkle flour, stirring, and cooking for another 1-2 minutes.
Add chicken stock, buffalo sauce, chicken, potatoes, and grated cheeses.
Stir constantly until cheese melts and bring soup to boil.
Once boiled, reduce heat and let simmer uncovered, stirring occasionally, 20-30 minutes or until potatoes can be pierced with a fork.
Garnish with sliced green onions, blue cheese crumbles, and a baguette.